1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to an image forming apparatus that determines a transfer voltage or a transfer current, and a control method thereof.
2. Description of the Related Art
An image forming apparatus forms an image to be output on a recording medium, and the contents of the image are generated by a computer program. In further detail, the image forming apparatus forms an electrostatic latent image by scanning light onto a photosensitive body, the electrostatic latent image is developed by a developer, and then the developed image is transferred and fixed on paper so that an image is formed.
FIG. 1 illustrates a transferring process of a conventional image forming apparatus.
As illustrated in FIG. 1, the conventional image forming apparatus includes a transferring device 2 and an attraction unit 1, and the transferring device 2 includes a plurality of transferring units 2a to 2d. The transferring unit 2a that is disposed closest to the attraction unit 1 among the plurality of transferring units 2a to 2d is established as a reference transferring unit, and a resistance value of the transferring unit 2a is obtained by detecting a current flowing therein so that an optimal transfer voltage or transfer current can be determined during a pre-printing process that is performed before printing on a printing medium.
The resistance value of the transferring unit 2a is characterized by a current therein corresponding to a voltage applied across a photosensitive body, a conveyor belt that passes through the corresponding transferring unit 2a, and a transfer roller disposed opposite to the photosensitive body across the conveyer belt. Knowing this resistance allows optimizing the energy to transfer toner developed on the charged photosensitive body to the printing medium.
Once the resistance value of the transferring unit 2a is determined, the conventional image forming apparatus ascertains a resistance value of the attraction unit 1 by detecting a current flowing therein responsive to a voltage applied thereto. The resistance value of the attraction unit 1 is the resistance of an attraction roller (ATTR) 1a that attracts the printing medium to the conveyer belt, and a driving roller that controls the printing medium to be moved to the transferring device 2 by the conveyer belt.
When the resistance of the attraction unit 1 is known, a current flowing therein is detected in response to a test voltage while the printing medium in the attraction unit 1. In this manner, a resistance value that corresponds to that of the printing medium is obtained. With such a recognized resistance value, an optimal transfer voltage for a transferring operation can be determined.
However, the conventional image forming apparatus determines the resistance value of the transferring unit 2a closest to the attraction unit 1, and therefore when power is applied to the attraction unit 1 to determine the resistance value thereof, a leakage current from the attraction unit 1 may interact with the transferring unit 2a so that the resistance value of the transferring unit 2a may not be accurately obtained.
As illustrated in FIG. 2, the conventional image forming apparatus obtains a resistance value of the transferring unit 2a during a period of t1 to t2, and obtains the resistance value of the attraction unit 1 during a period of t2 to t3 after the resistance value of the transferring unit 2a has been determined.
In the period of t4 to t6, a resistance value of the printing medium is ascertained so that an appropriate attraction current to each printing medium may be applied, and the appropriate attraction current is applied to the printing medium during a period of t6 to t7.
At the same time, a transfer current is applied to the transferring unit 2a during the period of t6 to t7 so as to transfer a developer onto the printing medium. In this case, the attraction unit 1 and the transferring unit 2a are located close to each other such that the applied current in each gives rise to a current leakage into the other, thereby causing an undesirable interaction therebetween.
Accordingly, the attraction current is leaked to the transferring unit 2a, and thus an attraction voltage cannot be maintained at an appropriate attraction voltage level, and the transfer current is leaked through the attraction unit 1, and thus a transfer voltage cannot be maintained at an appropriate transfer voltage level so that both of the attraction voltage and the transfer voltage become less than the required level, thereby causing errors in the attraction and transferring operations.
The above information disclosed in this Background Section is provided to facilitate understanding of the present general inventive concept in the context of certain shortcomings in the image forming art. The description above is not intended as an admission that such context of the described shortcomings is prior art under Title 35 of the United States Code.